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Coral Reefs in Latin America Coral Reefs: Definitions

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Coral Reefs in Latin America Coral Reefs: Definitions Coral Reefs in Latin America Coral Reefs: Definitions The primary criteria for classification as a reef are: 1) It is constructed of material of biological origin, mostly calcium carbonate. 2) It is a rigid structure due to interlocked and in-place framework elements. 3) It stands topographically above the surrounding seafloor and exerts some control on local oceanographic processes. http://cima.uprm.edu Importance of Coral Reefs • High Economic Value, $ 1.6 billion to the economy of Florida. Up to half of the GDP of some countries is supported by coral reefs • Storm Protection • Biodiversity Conditions for modern reef development: Modern reefs are highly dependent on the requirements of the main reef builders, scleractinian corals and calcareous algae, as follows: 1) Water must be warm, shallow, and of normal salinity: •shallow water (<100m): within the local photic zone. Both calcareous algae, and the zooxanthellae which live symbiotically within scleractinian corals, depend on light for photosynthesis •warm water (18 to 36°C; optimum 25 to 29°C) is required for the growth of hermatypic (reef-forming) scleractinian corals •normal marine salinity (22- 40 parts per thousand). 2) Bottom must be firm and not too much mud in the water •low terrigenous clastic (mud and sand) input: some reef-building organisms are killed by sand and mud. •stable and firm seafloor is needed for reef builders to attach Corals are animals! The individual polyp is an invertebrate of the phylum Cnidaria. Cross Section of a Coral Polyp The body is soft and tubular, with an oral opening surrounded by six (or multiples of six) tentacles. At night, these extend to trap plankton. The body wall mouth consists of three layers, the innermost of pharynx which (gastrodermis) contains zooxanthellae Stomach Zooxanthellae symbiotic photosynthetic single-celled algae • Contained within the coral gastrodermal cells • Use photosynthesis to create food for the coral host Symbiotic relationship between coral (animal) and zooxanthellae (plant) From zooxanthellae: Lipids, sugars, and O2 From coral: Nutrients, carbon dioxide & shelter Nitrogen and phosphorous derived from captured plankton are shared between symbiont (zooxanthellae) and host (coral). Scleractinian Corals • Hard corals or stony corals • Secrete calcium carbonate (CaCO3) • Most important group of organisms on a reef, because Scleractinian corals are reef building (= hermatypic). • Contain zooxanthellae. Reef activity is concentrated in the Photic Zone • The 'photic zone' is the uppermost part of the ocean, it reaches a maximum of 200 meters in the open sea, to which sunlight penetrates. This determines the depth to which photosynthesis can occur. • Scleractinian corals cannot grow - and reefs cannot form - if zooxanthellae cannot survive. Precipitation of Calcium Carbonate by Corals (1) The ocean is saturated with the three major polymorphs of CaCO3 (aragonite, calcite and magnesian-calcite). Yet, CaCO3 rarely precipitates spontaneously in seawater. As a result, biologically mediated CaCO3 precipitation by corals is the most important contributor to building reefs. Coral polyps absorb calcium ions from seawater and move them to the site of calcification, where they are deposited as aragonite. Aragonite Orthorhombic CaCO3 Crystal of twinned Aragonite from Spain SEM image of Aragonite. Precipitation of Calcium Carbonate by Corals (2) Calcium carbonate formation is described by the formula: +2 - Ca + 2HCO3 <=> CaCO3+ CO2+ H2O - (HCO3 = bicarbonate ion) The production rate of aragonite is thus related to the +2 - abundance of Ca + HCO3 in the water. The addition of CO2 to water yields bicarbonate through the following process: + - +2 CO2+ H2O <=> H2CO3<=> H + HCO3 + Ca (H2CO3 = carbonic acid) Free H+ lowers the pH ( i.e. makes the solution acidic). Calcium carbonate dissolves in weak acid, so unless the excess H+ is removed, no aragonite can precipitate. Stony corals remove excess H+ from seawater and allows aragonite to precipitate. Alcyonarian Corals • Soft corals • Internal skeleton • Large and feathery • Not reef building • Rely more on suspension feeding Calcareous Algae As important as corals in reef and beach building. Distribution is similar to that of coral. Approximately 30 marine species Early coloniser of tropical habitats, succeeded by sea-grasses Accounts for a significant amount of CaCO3 deposits. Produces up to 50% of all tropical beach sand Highly productive Udotea Halimeda Distribution of Reefs • Defined by environmental requirements: – Light –Clear water (areas poor in nutrients) – Warm constant temperature water, > 20 °C – Low turbidity (not off Amazon and Orinoco) • Thus, limited to within 30° North and South of equator Temperature Control 20°C = 68°F Global distribution of Coral Reefs Note that most of the reefs in Latin America are in the Caribbean and Greater Antilles, well north of the equator! Why? Biodiversity of Scleractinian= number of genera Maximum biodiversity is found in the Western Pacific and Indian oceans. Biodiversity of hard corals is much less in the Atlantic (and Caribbean) than in the Pacific 75% more genera and 85% more species in the Pacific compared to Caribbean. QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. Why is Biodiversity so low in Latin American reefs? Fringing Reef Fringing Reef Barrier ReefFringing Reef Radar image of Bora-bora barrier reef BarrierGreat Barrier Reef Reef, Australia Most famous reef on Earth. GBR extends 2 000 kilometers and covers an area of 35 million hectares on the north-east continental shelf of Australia. BGR covers an area that is bigger than Italy. Atoll Atoll • Seaward side: reef front and crest – Rise from depth to near the surface Typical Reef Profile – Typically steep – Major surge area; waves determine species – Finger-like projections – spurs • Back reef: beach and lagoon (reef flat) – Different assemblage of species than on seaward side – Coral rubble, sands, sea grass, patches of coral – Intertidal pools • Position determines growth form Growth forms of the coral Pocillopora damicornis Coral forms Branching Columnar Solitary Reef Reef Back reef Reef front Fore reef flat crest Waves and swell General model of a platform-margin barrier reef presented by James (1983). QAd2413c Typical reef profile Goreau and Land 1974 A. Pal.= Acropora palmata Discovery Bay Jamaica Reef flat Reef crest Reef front Back reef Reef crest Fore reef Reef flat Reef crest 1 2 1 2 Reef Front A = coarse sediments B = fine sediments C = daily temperature variation D = number of different species (according to H. Schumacher 1967) Evolution of Reefs and Formation of Atolls Darwin’s sequenceAtoll evolution of Atoll formation (Darwin) First: fringing reef Second: barrier reef Third: Atoll • About 14% of the area of the world’s coral reefs are found Caribbean Reefs here. • Fringing and patch reefs are common around islands, on the side facing the prevailing winds (windward side). • There is a long barrier reef system off Belize (approximately 220 kilometers) and the Andros barrier reef (approximately 176 kilometers) in the Bahamas. Belize • Territorial disputes between the UK and Guatemala delayed the independence of Belize (formerly British Honduras) until 1981. Guatemala refused to recognize the new nation until 1992. Tourism has become the mainstay of the economy. • Area: total: 22,966 sq km slightly smaller than Massachusetts • Climate: tropical; very hot and humid; rainy season (May to November); dry season (February to May) • Elevation extremes: lowest point: Caribbean Sea 0 m highest point: Victoria Peak 1,160 m • Geography - note: only country in Central America without a coastline on the Pacific • Population: 272,945 • GDP - per capita: purchasing power parity - $4,900 (2002 est.) • Languages: English (official), Spanish, Mayan, Garifuna (Carib), Creole From http://www.cia.gov/cia/publications/factbook/geos/bh.html The Belize Barrier Reef and the three offshore atolls [STS060-85-W, 1994]. Belize • Bank or bank-barrier reefs are common. Atolls are also found. • Reef Reefs of Greater & development is often greater on the smaller, low Lesser Antilles islands with low rainfall and little sedimentary runoff such as Barbuda, Antigua, St. Croix, Grande Terre and the Southern Grenadines. • The Greater Antilles (Cuba, Hispaniola and Puerto Rico) generally have larger reefs than the Lesser Antilles (Putney 1982). Reefs of Florida and the Greater Antilles Florida and Bahamas Cuba Reefs in the Western Atlantic Brazil • The distribution of coral reefs in the South Atlantic is limited to tropical areas along the coastline and offshore islands of Brazil. • According to UNEP/IUCN (1988) the Brazilian coral fauna has long been considered of interest on account of its high proportion of endemic species. • Some 3,000 kilometers of coast have reefs. Ten of the 18 hermatypic coral species known from Brazil are endemic. http://www.ramsar.org/w.n.brazil_coral_atlas.htm Brazil Reefs • Two main coral reef localities are found on the Brazilian coast. – Grupo Recifal do Cabo São Roque, from Cabo de São Roque to Natal in Rio Grande do Norte State, including the Fernando de Noronha archipelago and the Rocas atoll – Coral reefs along the south coast of Bahia State (the Abrolhosa Archipelago), the richest and most developed coral reef formation in the region. • Coral reefs also occur between Natal and the São Francisco river mouth and on the latitude of Salvador Bahia (both usually associated with calcareous reefs). • The northeast coast formations
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